Coenzyme models. Part 36. Hydroxide-mediated disproportionation of a lipophilic acridinium salt in a micellar system

Abstract

We have found that N-dodecylacridinium ion (DodAc⁺) is rapidly disproportionated to N-dodecylacridone (DodAcd) and N-dodecylacridan (DodAcH)via hydroxy-adduct (DodAcOH) in the presence of cationic (CTAB) or non-ionic (Brij-35) micelles. Product analyses show that two moles of DodAc⁺ produce one mole of DodAcd and one mole of DodAcH and the hydrogen is directly transferred from DodAcOH to DodAc⁺. The reaction is similar to oxidation of alcohols by NAD⁺ model compounds. Kinetic studies show that the reaction consists of two steps, the first an equilibrium for formation of the hydroxy-adduct and the second disproportionation to RAcd and RAcH. The first step is efficiently accelerated by CTAB and Brij-35 and the association constants (K) are enhanced by 10⁵–10⁶-fold. On the other hand, the second step is less susceptible to the micellar environment and is not base-catalysed. Thus the micellar effect on the first step is responsible for the overall rate enhancement. This is the first example of a micellar effect on the hydroxide ion-mediated disproportionation of heteroaromatic nuclei.